Captive Portal issue

I can't see that the captive portal will have any bearing on traffic on the same VLAN, the portal will only impact outgoing traffic - does the problem still exist if you don't authenticate? if these are wifi clients then I've seen client isolation having this type of affect.

Regards

Thank you, it was access point isolation

Normally you should not have this problem on same vlan, does it still exist if your on another vlan without user portal? Maybe something other is blocking it, like endpoint client (AV) or swicth has something disabled. Whats also possible on wifi network like from unifi there is option you can isolate clients from each other, so keep  that in mind.